Intense energetic gas discharge



March 1, 1960 J. 5. LUCE INTENSE ENERGETIC GAS DISCHARGE 3 Sheets-Sheet 1 Filed July 15, 1958 m zm m JTUHT 55:9;

T EN wUmDOm m o INVENTOR. John S. Luce ATTORNEY March 1, 1960 .1. s. LUCE 2,927,232

INTENSE ENERGETIC GAS DISCHARGE Filed July 15, 1958 3 Sheets-Sheet 2 RF. VOLTAGE 75 SOURCE GAS 5 59 GAS SOURCE SOURCE INVENTOR. John S. Luce firw 4'. WM

ATTORNEY March 1, 1960 J. s. LUCE INTENSE ENERGETIC GAS DISCHARGE 3 Sheets-Sheet 3 Filed July 15, 1958 RF. VOLTAGE SOURCE GAS SOURCE TO VACUUM PUMP INVENTOR.

John S. Luce aired States Patent ice INTENSE ENERGETIG GASiDISCHARGE John S. Luce, Oak Ridge, Tcnn.,.assignor tothe: United States of America as represented by theUnited-States Atomic Energy Commission Application July 15, 1958; Serial No. 748,771

13 Claims. (Cl. 31363) This invention relates to a device for producing an energetic deuterium or tritium arc.

Energetic arcs have been developed for use as a dissociating mechanism in thermonuclear devices. An example of the efiiciency of a high current or energetic are as a dissociating mechanism is setforth in'my co-pending applications Serial No. 728,754, filed April 15, 1958, entitled Method and Apparatus for Trapping Ions in a Magnetic Field, and Serial No. 738,242, file'd May 27, 1958, entitled Device and Method for Producing a High Intensity Arc Discharge. The latter application relates to an energetic carbon arc, and the former application relates to the use of the energetic carbon are in a thermonuclear device. In one such thermonuclear device, high energy molecular ions such as D for example, .are injected into a confining magnetic field perpendicular to the lines of magnetic force. At some point in-the orbit of these ions in the magnetic field, a portion of them are caused to be dissociated and/ or ionized by the carbon arc to form atomic ions. These resultant atomic ions have one-half the momentum of the original molecular ions that have an atomic weight of two and hence have onehalf the radius of curvature in the field. The radius of curvature of the atomic ions depends upon the atomic weight of the injected molecular ions. It the center of the orbits of these atomic ions coincides. with the axis of the magnetic field, the ions will circulate in aring. If the center of the orbits and the axis of the machinedo not coincide, the atomic ion orbit will-precess about the point of origin of the atomic ion. The ions will circulate until a charge exchange occurs with one of the neutral gas atoms in the system.

The energetic carbon ion arc produces low pressures when in operation which, in part, accounts forits high efficiency as a dissociating mechanism. Despitethe many desirable characteristics of the energetic carbon arc, one basic disadvantage exists. Energetic ions in the carbon arc collide with carbon ions and may lose much of their energy by Bremsstrahlung and ionization. The amount of energy lost in such processes is directly proportional to the atomic number of the ions, so that for carbon ions, the losses may be substantial. It is very important in the process of building up a thermonuclear-plasma that any losses of the energy imparted to the particles in the volume be held to a minimum.

Despite the disadvantage mentioned, the carbon-arc has been utilized heretofore because conventional gas are discharges cannot be operated in high magnetic fields at pressures low enough for them to become effective dissociating mechanisms. At normal operating pressures such gas arcs will not cause any atomic ions to be trapped in a magnetic field because of the large number of charge exchanges that take place.

Another problem associated with gas arcs is the intense heating of the electrodes with a consequent influx of impurities into the are.

creating a thermonuclear plasma, the shortcomings of conventional gas arcs as dissociating agents, the electrode heating problem, and the disadvantage of the car bon ion discharge,.applicant has as a' primary object of this invention production of anflenergetic gas'discharge' or are which is capable of dissociating a substantial percentage of molecular ions passed therethrough.

An important object of the invention is production of a highly energetic are which will not be characterized by large Bremsstrahlung energy losses.

It is another object of this invention to provide a device for operating a deuterium arcdischarge under low'pressures, and with a minimum of electrode heating.

These and other objects and advantages will be apparentfrom a consideration of the following detailed specification and the accompanying drawings wherein:

Fig. 1 shows a cross-sectional view of a device for producing an energetic deuteriumarc.

Fig. 2 shows a cross-sectional view of the hollow cathode of Fig. 1 and the electron paths therein.

Fig. 3 shows a cross-sectional view offa' device for producing an energetic deuterium reflux-type arc, discharge, and

Fig. 4 shows a;cross=sectional.view of another embodiment for producing an energetic deuterium refiux-typearc discharge.

The objects stated above have been achieved in the present invention by providing. novel means for producing an unique energetic arc in deuterium, which has a low atomic number. and therefore low Bremsstrahlung and ionization losses. This unique arc has also proved capable of substantial dissociation of'molecular ions, unlike conventional deuterium discharges.

In accordance with the present invention a hollow cathode is provided, deuterium or other gas is introduced into the interior of the cathode, and by regulating the rate of gas flow, it is possible ,underproper pressure conditions to provide anarcdischarge which runs from the inner surface of the cathode. Under. theseconditions, adequate space-charge neutralization is provided. inside the cathode but not inthe main arc volume.

The arcs described hereinoperate under substantially high voltage and current and as a. result, heating of the electrodes is a problem. This problem has been solved by using electrodes which are tungsten or any other conductive andhigh melting point material that .is also. a good thermal conductor.v Carbon may be used for. the anodes but is undesirable for the reason that it is a poor thermol conductor under high temperature and it is not possible to provide sufiicient cooling of. the:anodes to bore of the jacket, may suitably be undersized to the extent that heating to severalhundred-degrees isrequired for insertion of. the electrodes. During operation of A such a jacketed electrode, the differential expansion pro'-' duces a very tight fit and therefore good heat. transfer.

Under low pressure, for example 3 10- mm. Hg. or v A lower, the arc in the modification of. Fig. l is a hollow cylinderand the arccurrent iscarried in. this. cylinder close to the inside cathode .wall. The are depends upon emission across the magnetic field Withinthe. hollow.

cathode. .No decrease in emission occurs .when the .arc is operated in a strong magnetic field, for example, a field of 6000 gauss. The arcs of Fig. 3 andFi'g. 4 are not hollow, but they also depend upon. emissionacross. the magnetic field within hollow cathodes.

There are at least two unique :characteristics' of, the,

With a knowledge oftheproblems-associated withdeuterium arcs described herein which distinguishthem from other arcs and which permit them to be operated under low pressure and to be very energetic. The first characteristic is the cross field emission, achieved by provision of a large surface area from which electrons may enter the system. The deuterium gas which is fed into the the inside of the hollow cathode is completely ionized before it leaves the cathode. Since there is adequate space-charge neutralization inside the cathode, it is possible to decrease the pressure Without affecting the emission characteristics of the arcs. The second characteristic of the arcs is the existence of an axial potential gradient in the arcs. Electrons are accelerated radially from the inside wall of the cathode. Some of those electrons which suffer collisions before returning to the wall are trapped close to the cathode inside wall and thereupon are drawn out of the cathode by this axial potential gradient.

Referring now to Fig. 1, which illustrates one modification of apparatus in which the principles of this invention may be carried out, a hollow elongated cup-shaped cathode electrode 1 is mounted in block 3, and a hollow elongated cup-shaped anode electrode 2 is mounted in a block 4. Floating cathode shields 5 and 6 are mounted by insulators 8 and 9, respectively, to an outer chamber wall 13. Anode shield 7 is mounted by an insulator 10 to the chamber wall 13. A strong magnetic field, for example, 6000 gauss, is provided by magnets 11 and 12, the direction of the field indicated by the arrow H. Deuterium or tritium gas is fed from a source 14, and through tube 15 to the inside of hollow cathode 1. The cathode and anode are cooled by a cooling fluid which is passed through tubes 33 from a source not shown.

An outer vacuum chamber 21 is formed by the walls 13 and is connected to a vacuum pump by the tube 23. An inner vacuum chamber is formed by the walls 17, as shown, and is connected to a vacuum pump by the tubular member 22. Bafiies 18 are provided adjacent the cathode 1, the bafiies 19 are provided adjacent the anode 2. These baflles are insulatingly supported. An arc initiating assisting means such as an R.F. voltage source 31, which may be a conventional welding source, is connected at one end to anode 2 by a lead 32, and at its other end to cathode 1 by lead 30, switch 29, and lead 28. An operating potential is connected to the anode and cathode by a variable D.C. source, such as a variabletap multi-cell battery 25. Battery is connected at one side to cathode 1 by a lead 24, and is connected at its other side to anode 2 by a switch 26, and lead 27.

The blocks 3 and 4 are insulatingly supported on the chamber wall 13 by means not shown. In one example of the device of Fig. 1, the cathode was 5 inches long, had an outer diameter of 0.75 inch, and an inner diameter of 0.375 inch. The anode was 5 inches long, had an outer diameter of 0.75 inch, and an inner diameter of 0.5 inch.

In operation of the device of Fig. l at startup, gas is fed from source 14 and through tube 15 to the cathode 1 until the pressure in the cathode and chamber 20 reaches a value of approximately 3 10- mm. Hg, and a R.F. voltage source 31 is then applied across the electrodes 1, 2. Also a D.C. voltage source 25 is connected across the electrodes. The are is initiated at the faces 34 and of the cathode and anode, respectively. After the are 16 is initiated, the R.F. source 31 is disconnected and the gas feed is reduced until the arc moves from the faces 34 and 35 of the electrodes into the interior of the electrodes. The gas feed to the arc is maintained at a rate just sufl'icient to provide complete spacecharge neutralization within the hollow cathode, while the pressure in chamber 20 is gradually reduced until it reaches a value approximately 3 10- mm. Hg or lower. The pressure in outer chamber 21 is maintained at a value of approximately 10- mm. Hg. The pressure difference under operating conditions between the chambers is maintained at a constant value.

During all stages of operation of a device having the dimensions referred to above, a magnetic field strength of about 6000 gauss is maintained by the magnets 11 and 12. As the pressure in chamber 20 is lowered, the voltage across the electrodes is increased and when the pressure in chamber 20 reaches a normal operating value, for example 3 10- mm. Hg, the voltage across the electrodes 1 and 2 is approximately 400 volts and the arc current reaches a value of approximately amperes.

In order for the arc to operate from within the cathode and under the preceding conditions, it is necessary that the gas flow be maintained at a rate sufliciently low that adequate space charge neutralization is provided inside the cathode but not in the main volume, and that the bore of the cathode is in accurate alignment with the magnetic field.

As discussed above, the arc depends upon cross-field emission within the cathode. Because of the cross-field emission, the arc requires a much higher applied voltage than the carbon arc of my co-pending application Serial No. 738,242, aforementioned. As the gas input is re duced, the voltage continues to be increased.

Fig. 2 shows an example of typical electron paths within the cathode. As mentioned above, electrons are accelerated radially from the inside wall of the cathode. Some of those electrons which sufier collisions before returning to the wall are trapped and drawn out of the cathode by an axial potential gradient in the arc and thus move toward the anode. During the course of travel toward the anode, more collisions occur throughout the length of the arcs. Each of these collisions with gas molecules causes ions to be formed and the arc is thus formed and sustained. These ions are accelerated along the magnetic field toward the cathode by the potential gradient in the arc. Since the motion of the ions is not random but carries them rapidly toward the cathode, diffusion and recombination will be greatly reduced. To exploit this advantage, bafiies 18 and 19 are provided between the electrodes and the working volume of the are. A large number of the ions that are accelerated into the cathode and that recombine will then be prevented from flowing back as neutral particles by differential pumping between chambers 20 and 21.

Arcs have been operated with other gases, for example, air, hydrogen, argon, nitrogen, and helium and may be operated with any gas. However, the use of deuterium or tritium is needed for thermonuclear reactions.

The anode need not be cup-shaped but may be solid instead. Anode heating and thus sputtering of impurities may be minimized by use of a rotating anode whereby the electron bombardment is spread over a larger surface area.

The are described above is an eificient dissociating device. It has been determined that this are has breakup efliciencies of 25% when used for dissociating 20 k.e.v. deuterium molecular ions.

As discussed above, the are formed by the device of Fig. 1 is a hollow arc. In addition to its usefulness for dissociating and/or ionizing molecular ions, this are is useful in reducing the instreaming of cold neutrals from the vessel walls into the plasma of a thermonuclear machine such as disclosed in my co-pending application Serial No. 7 8,754, aforementioned. In using the deuterium arc of Fig. 1 in the machine therein described, the magnetic mirror coils at the ends of said machine permit the hollow arc to be enlarged in the center portion of the machine where the molecular ions are injected. Under such conditions the thermonuclear plasma is confined within the hollow arc and some of the energetic particles from the plasma will penetrate the arc and strike the walls of the machine. However, low energy neutrals resulting from this bombardment and other processes can not pass back through the arc barrier and enter the plasma without being ionized in the are. The ions thus formed are then pumped out of the machine by the well-known pumping action of arcs.

Referring now to Fig. 3, which illustrates another modification of apparatus in which the principles of this lnvention may be carried out, a first hollow cup-shaped tungsten cathode electrode 40* is mounted in a copper block 42. The copper block 42 is enclosed in a casing 44 which is insulatingly supported in the outer chamber wall 62. A second hollow cup-shaped tungsten cathode electrode 41 is mounted in a copper block 43. The copper block 43 is enclosed in a casing 45' which 1s insulatingly supported in the outer chamber wall 62. Floating apertured cathode shields 46,. 47, and 48 and the apertured electron reflector 49 are insulatingly mounted in the inner chamber wall 54 and are disposed adjacent the first cathode 40. Floating apertured cathode shields 51, 52, and 53, and apertured electron reflector 50 are insulatingly mounted in the inner chamber wall 54 and are disposed adjacent the second cathode 41. These cathode shields and electron reflectors act as baflies between an inner vacuum chamber 80 and an outer vacuum chamber 81. A hollow elongated anode electrode 73 is insulatingly mounted to the inner chamber wall 54 by means not shown.

A strong magnetic field is provided by magnets 60 and 61, the direction of the field indicated by the arrow H. Deuterium or tritium gas is fed from a source 58, and through tube 56 to the inside of hollow cathode 40. Also, deuterium or tritium gas is fed from a source 59, and through tube 57 to the inside of hollow cathode 41.

The inner vacuum chamber 80 is formed by the. walls 54, as shown, and is connected to a vacuum pump by the tube 55. The outer vacuum chamber 81 is formed by the walls 62 and is connected to a vacuum pump by the tube 63. An arc initiating assisting means suclr as an RF. voltage source 74, which may be a conventional Welding source, is connected at one end by leads 71 and 73, and by leads 71 and 72 to cathodes 40 and 41, respectively, and at its outer end by lead 75, switch- 76, and lead 77 to anode 78. An operating potential, such as a variable-tap multi-cell battery 61, is connected at one side by leads 64 and 66, and leads 64 and 65 to cathodes 40 and 41, respectively, and is connected at its outer side to anode 78, by lead 68, switch 69, and lead 70.

In one example of the device of Fig. 3, the cathodes 40 and 41 were 5 inches long, having an inner diameter of 0.625 inch. The hollow anode 78 was 8 inches in length having an inner diameter of 2 inches. For long arcs up to 6 feet in length, the anode has diameters up to 6 inches in diameter. The length of. the anode is not critical to the operation of thedevice set forth in this embodiment. The only lower limit is that imposed by the dissipation of the energy caused by electrons striking the anode. It is generally made long with respect to the diameter so as to permit difierential pumping to provide a lower pressure in the central region than at the cathodes.

In operation of the device of Fig. 3 at startup, gas is fed from source 58, through tube 56 to cathode 40, and gas is fed from source 59, through tube 57 to cathode 41 until the pressure in the cathodes and chamber 80 reaches a value of approximately 3 10 mm. Hg, a RF. voltage from source 74 is then applied across cathode 40 and anode 78, and across cathode 41 and anode 78, and a DC. voltage from source 67 is applied across cathode 40 and anode 78, and across cathode 41 and anode 78. The are is initiated at the faces 82 and 83 of the cathodes 4G and 41, respectively. After the arc 7d is initiated, the RF. source 74 is disconnected by switch 76, and the gas feed is reduced untilthe arc moves from the faces 82 and 83 of the cathodes into the interior of said cathodes. The gas feed to the arc is maintained at a rate sufiicient to provide complete der normal operating conditions is maintained at a constant 1 value.

During all stages of. operation of a device having the dimensions. referred to above, a magnetic field'strength is maintained at a selectedvalue inthe range from approximately 3000 to 60001gauss by the magnets 60 and 61. The-reflux-type are. produced by the embodiment of Fig.3 has a much higher resistance than the one of Fig. l. and has been operated at voltages up to one kilovolt, with are currents up to 100 amperes. The energies present in the are are directly proportional to the applied voltage.

In order for the arc to operate from within the cathodes .and under the preceding. conditions, it is necessary, as in .Fig. 1, that the gas flow be'maintained at a rate sufliciently low so that adequate space charge neutralization is provided inside the cathodes but not in the main volume, and 'that the bores of the cathodes are in accurate alignment with the magnetic field.

The embodiment set forth in Fig. 3 does not have as great a heating problem as that of Fig. 1'. The nature of. the discharge of Fig. 3 is such that the electrons in the discharge oscillate between the. cathodes until they suffer a collision and gradually precess to various portions of the inner surface of the hollow anode. Cooling tubes are also necessary forthe device of Fig. 3 and for Fig. 4 which operates in a manner identical to that of Fig. 3. These cooling tubes are not shown in Fig. 3 or'Fig. 4 for the sake of clarity. The method of jacketing the tungsten cathodes 40 and 41 with copper is the same as that described above, which provides good heat transfer for the heating that does occur.

The cathode shields and electron reflectors of Fig. 3 which serve as baflles, as mentioned above, serve thesame purpose as the .baffles of Fig. l. A floating plate may be substituted for one of the cathodes of Fig. 3, and since such ,a plate would assume the potential of the cathode the resulting are would operate in a similar mannerto thatde'scribed above forFig. 3.

The are discharge provided by the apparatus of Fig. 3 need not necessarily be collimated in a straight line but may be curved if proper provision is made for the magnetic field and the electrode configuration. Fig. 4, which illustrates another embodiment of the invention, shows the structure for operating a curved are 98 in the form of a toroid. The anode is generally a toroid with one segment removed to permit insertion of a curved hollow cathode and the necessary apertured shields and electron reflectors. Emission takes place within both ends of the cathode in such an arrangement. The operation of'the device of Fig. 4 is identical to that of Fig. 3.

In the embodiment of Fig. 4, a curved tungsten hollow cathode electrode 85 is'mounted in a copper jacket 104 in the same manner as described above. A circular curved hollow anode electrode 86 is mounted by'means not shown to the outer chamber wall 96.- The respective ends of the anode 96 are disposed in confronting relation to the end faces 116 and 117 of the hollow cathode. Apertured cathode shields 8S and 89, and apertured electron reflector 87 are insulatingly mounted in the inner chamber walls $3, and are disposed adjacent the cathode face 117. Apertured cathode shields 90 and 91, and

apertured electron reflector 92 are insulatingly mounted. V

in the inner chamber walls 93, and are disposed adjacent the cathode face 116. p

v A strong magnetic field, for example a selected value in the range from 3000 to 6000 gauss, is provided by the magnetic coils 103, The magnetic coils 103 are dis'-' posed around the hollow anode 86 and end toend for the entire length of the anode. netic field is indicated by the arrow H.

Deuterium or tritium gas is fed from source 100 and through tube 99 to the interior of the central portion of the hollow cathode. Feed tube 99 is enclosed by a tubular member 105. An inner vacuum chamber 102 is formed by the walls 93, and is connected to a vacuum pump by tubular member 95 connected to wall 93. An outer vacuum chamber 101 is formed by the walls 96 and is connected to a vacuum pump by the tubular member 97. An arc initiating assisting means 112, which is a R.F. voltage source such as a conventional welding source, is connected at one side to the cathode 85 by lead 111, and is connected at its other side to the anode 86 by lead 113, switch 114, and lead 115. A variable D.C. operating potential 107, such as a variable-tapped multi-cell battery, is connected at one side to the cathode 85 by lead 106, and is connected at its other side to anode 86 by lead 108, switch 109, and lead 110.

The electron reflectors 87 and 92, and the cathode shields 88, 89 and 90, 91 act as baffies to provide differential pumping between the inner and outer chambers in a manner similar to the device of Fig. 1.

For a discussion of the operation of Fig. 4, reference is made to the operation of Fig. 3 above which operates in an identical manner. The only difference between the respective devices is the shape of the arcs, and Fig. 4 shows a single hollow cathode with electrons being emitted out of each end of said cathode while Fig. 3 shows the use of two spaced cathodes.

The are discharges of Fig. 3 and Fig. 4 can be used to provide a source of energetic ions and electrons, and for the dissociation and/or ionization of molecular ions. Also a portion of the discharge can be pinched-off by magnetic mirror coils and compressed sufliciently to multiply the energy and thereby achieve ignition of a thermonuclear plasma.

An advantage of the discharges of Fig. 3 and Fig. 4 is that pinch-type discharges may be induced without causing the intense pinch current to impinge in concentrated areas upon the electrodes. Actually at some point dur ing the pinch operation in the toroidal geometry of Fig. 4, the discharge would not strike the cathodes at all. This would substantially reduce heating and erosion problems associated with electrodes and the problem of introducing extraneous material into the discharge.

This invention has been described by way of illustration rather than limitation and it should be apparent that the invention is equally applicable in fields other than those described.

What is claimed is:

1. The method of producing an energetic electrical discharge, which comprises establishing a magnetic field oriented in a selected direction within an evacuated region at a pressure of approximately mm. Hg, initiating an arc discharge parallel to the direction of said field between the face of an elongated hollow cathode electrode and a hollow elongated anode electrode by applying a. DC. potential between said electrodes, while supplying a feed gas to said hollow cathode electrode, and by temporarily applying an arc initiating assisting means between said electrodes, removing the assisting means after the arc is struck, cooling said electrodes, varying rate of feed of said gas until the are dis charge moves from said cathode face to terminate inside said hollow cathode whereby complete space-charge neutralization occurs within the cathode, and simultaneously lowering the pressure in said region and increasing said potential to provide the desired arc current, whereby electrons radially accelerated from the inside surface of said hollow cathode across said field are trapped in a region adjacent the inner surface of said cathode and accelerated toward the anode by a potential gradient in the arc discharge.

The direction of the mag- 2. The method set forth in claim 1 in which said feed gas is deuterium.

3. The method set forth in claim 1 in which the feed gas is tritium.

4. The method of producing an energetic electrical discharge which comprises establishing a magnetic field oriented in a selected direction within an evacuated region; initiating an arc discharge parallel to the direction of said field between an elongated hollow cathode electrode and a confronting hollow cup-shaped anode electrode by feeding deuterium gas to the end of said hollow cathode distal from said anode, applying a potential between said electrodes, and temporarily applying an arc initiating assisting means between said electrodes; removing said assisting means after the arc is struck; cooling said electrodes; reducing said feed gas flow to cause said discharge to terminate within said cathode; and varying said potential and lowering the pressure within said region to establish a space-charge neutralization condition within said cathode by virtue of cross field electron emission from the inner surface of the hollow cathode at a selected potential and pressure.

5. The method of producing an energetic electrical discharge which comprises establishing a magnetic field oriented in a selected direction within an evacuated region; initiating an arc discharge parallel to the direction of said field between a first elongated hollow cathode electrode, a confronting second elongated hollow cathode electrode and within a hollow elongated anode electrode disposed between said cathodes by feeding deuterium gas to the ends of said hollow cathodes distal from said anode, applying a potential between said electrodes, and temporarily applying an arc initiating assisting means between said electrodes; removing said assisting means after the arc is struck; cooling said electrodes; reducing said feed gas flow to cause said discharge to terminate within said cathodes; and varying said potential and lowering the pressure within said region to establish a space-charge neutralization condition within said cathodes by virtue of cross field electron emission from the inner surfaces of the hollow cathodes at a selected potential and pressure.

6. The method of producing an energetic electrical discharge which comprises establishing a magnetic field oriented in a selected direction within an evacuated region; initiating an arc discharge parallel to the direction of said field between both ends of a circular curved hollow cathode electrode and within a hollow circular curved elongated anode electrode, the respective ends of said anode being disposed adjacent and confronting the ends of said hollow cathode, said initiating being accomplished by feeding deuterium gas to the inside of the central portion of said cathode, applying a potential between said electrodes and temporarily applying an arc initiating assisting means between said electrodes; removing said assisting means after the arc is struck; cooling said electrodes; reducing said feed gas flow to cause said discharge to terminate within the ends of said cathode; and varying said potential and lowering the pressure within said region to establish a space-charge neutralization condition within said cathode by virtue of cross field electron emission from the inner surface of the hollow cathode at a selected potential and pressure.

7. A device for establishing a high-intensity or energetic gas are discharge which comprises an enclosed chamber, means for evacuating said chamber to a selected pressure, an elongated hollow cathode electrode and an elongated hollow anode electrode having a common axis and spaced apart within said chamber, means for establishing a magnetic field within said chamber, said magnetic field having a direction parallel to said axis, means for initiating and maintaining an energetic arc discharge between said electrodes comprising, a source of gas, means for feeding said gas at a controlled rate to the inside of said hollow cathode where it is completely ionized, means for cooling said electrodes, a first source of potential connected between said electrodes for temporarily assisting in the initiation of an arc discharge directly between said anode and the inner surface of said cathode, and a variable voltage source connected between said electrodes for varying the intensity of said discharge, whereby said controlled gas feed causes space-charge neutralization only within said hollow cathode to form a substantially hollow energetic are.

8. The device as set forth in claim 7 in which said chamber is provided with an inner chamber, an outer chamber which encloses said inner chamber, and wherein said evacuating means comprises separate pumps connected to said outer and inner chambers, and axially aligned bafiles mounted adjacent each of said electrodes whereby neutral particles formed at the electrodes are prevented from entering the inner chamber by the resulting difference in pressure existing between the inner and outer chambers.

9. The device set forth in claim 8, wherein the pressure is maintained at a pressure of substantially 3 10' mm. Hg in the inner chamber, the pressure in the outer chamber is maintained at a pressure of substantially 3X10- mm. Hg, the voltage source is maintained at substantially 400 volts, the magnetic field is maintained at a selected value in the range from 3000 to 6000 gauss, and the feed gas is deuterium, whereby an energetic arc of approximately 100 amperes is maintained.

10. The device set forth in claim 7 in which there is provided a second elongated hollow cathode in confronting relation with the other cathode with the hollow anode 'disposed between said cathodes,a second source of gas, means for feeding said second gas source to the inside 1 of said second cathode, and means for connecting said assisting means and said variable voltage source between said anode and said second cathode.

11. The device set forth in claim 10, wherein the pressure is maintained at a pressure of approximatelyB X'10-5 mm. Hg, in the chamber, the voltage source is maintained at a value of approximately 1000 volts, the magnetic field is maintained at a selected value in the range from 3000 to 6000 gauss, and the feed gas is deuterium, whereby an energetic arc of approximately amperes is maintained.

12. The device set forth inclairn 7 in which the anode is cup-shaped.

13. The device set forth in claim 7 in which said cathode is curved andhollow throughout its length, the anode is curved and hollow throughout its length with its respective ends being in confronting relationwith the respective ends of said cathode, and the feed gas is fed to the central inside portion of said cathode, whereby electrons are emitted from both ends of said cathode to thereby set up an oscillating discharge between said cathode ends and through said anode.

Foster Mar. 11,1958 Martina Apr. 22, 1958 

